1. Field of the Invention
Methods consistent with the present invention relate to a phase commutation method of a Brushless Direct Current (BLDC) motor, and more particularly, to a phase commutation method of a BLDC motor that minimizes noise and vibration by accurately controlling phase commutation timing.
2. Description of the Related Art
A BLDC motor is a motor that uses a rectifier circuit composed of switching elements rather than mechanical elements such as a commutator and brushes. BLDC motors are characterized in that there is no need to replace brushes due to abrasion and noise and electromagnetic interference levels are low.
BLDC motors are typically used in products such as washing machines and compressors for use in refrigerators and air conditioners, which require high-performance, variable-speed operation.
To run a BLDC motor, the flux of a stator in the BLDC motor must be controlled to be at an electrical angle of 90 degrees or at any other suitable electrical angle with respect to the flux produced by a permanent magnet in a rotor of the BLDC motor. To accomplish this, the position of the rotor must be constantly detected to determine switching states of switching elements in the inverter and determine a position of the stator, where flux is to be produced, according to the detected rotor position. A resolver, an absolute encoder, a hall sensor or the like may be used to detect the rotor position. However, it is difficult for BLDC motors in compressors for refrigerators and air conditioners to use sensors due to environmental factors such as temperature and pressure, and therefore the BLDC motors use a sensorless method for detecting the rotor position from a voltage or current applied to the motors.
Driving methods of BLDC motors can be classified into a rectangular current waveform method and a sinusoidal current waveform method according to the waveforms of phase current applied to the motors.
In the sinusoidal current waveform driving method, the rotor position can be detected by detecting all three-phase voltages and currents. Generally, rotor position information of a mechanical angle corresponding to one period (i.e., 360 degrees) for compressors of refrigerators, air conditioners, or the like requires a resolution of 10 to 12 bits.
Compressors of refrigerators, air conditioners, or the like have a very large variation in load applied to a motor for each rotation of the motor due to consecutive operations of refrigerant gas such as intake, compression, and discharge. When the BLDC motor performs 10 to 12 phase commutations while rotating one turn (i.e., while rotating through a mechanical angle corresponding to one rotation), it is necessary to correctly determine the time when each phase commutation is performed and the time when position detection is performed.
However, conventional BLDC motor phase commutation methods have not provided how to effectively or correctly determine when to perform a first phase commutation of the next period after the BLDC motor rotates through a mechanical angle corresponding to one rotation, so that noise and vibration is severe when the phase commutation method is used for inverter refrigerators or the like having a large variation in load applied to motors.
In addition, in the conventional phase commutation methods, when the BLDC motor operates stably after switching to sensorless mode, it performs phase commutation in the same manner as when the BLDC motor is in initial startup mode. Thus, the conventional phase commutation methods cannot perform phase commutation taking into consideration the characteristics of different operating modes of the BLDC motor.